Recent advances and challenges of emerging solar-driven steam and the contribution of photocatalytic effect

In recent years, solar-driven steam materials and systems for water desalination and decontamination have received increasing attention from the scientific community. Notwithstanding the fundamental scientific achievements reached on this topic, numerous technological concerns still remain to be addressed, including heat loss, radiation reflection, low degree of purification of condensed water, biofouling, and salt accumulation on the surface. In this report, we critically reviewed the most recent advances in the engineering of solar-driven steam materials and the main technology challenges which may limit their large-scale application. First, different classes of materials, e.g., inorganic semiconductors, carbonaceous materials, polymers, and surface plasmon resonance metals, are compared in terms of the mechanistic pathways to generate steam vapor and condensed to freshwater on their surface. Then, the main approaches to tackle the technology shortcomings of solar-driven steam systems are discussed in depth. For instance, in terms of salt accumulation, several strategies were proposed such as solar-driven surfaces with ion exchange or/and salt dissolving, an inversion system to remove the salt from the active surface, and salt rejection surfaces. To enhance the photothermal process and limit the reflection of light, thermal insulators, reflective layers, and 3D/pyramidal photoabsorbers were proved to be excellent strategies. The review addresses as well the recent research regarding hybrid systems by incorporating photocatalysis effect in solar-driven water evaporators. Photocatalyst addition endows the surface of evaporators with unique properties, such as the radical oxidation of organic pollutants and microbial inactivation, resulting in reduced fast biofouling and condensed waters with higher purity. Finally, the remaining challenges and prospects for future developments are critically discussed.